1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing hollow resin products, such as hoses and pipes, by blow molding.
2. Description of Related Art
Hoses to be provided in the engine room of an automobile, such as a defroster hose, an air hose, a radiator hose, etc. are curved two-dimensionally or three-dimensionally as shown in FIG. 4 to facilitate the fitting therein. Such a complicatedly curved resin article is conventionally produced by blow molding which has steps of: making a parison by cutting a resin material extruded from a die head of an extruder; feeding the parison into a cavity of a mold; and injecting compressed air into the parison. The most difficult step in the blow molding is the step of feeding the parison into the cavity of the mold (ordinarily a lower mold). With respect to this step, Japanese Laid Open Publication No. 53-56262 suggested moving the mold, and Japanese Laid Open Publication No. 55-21239 suggested moving the die head of the extruder. However, the necessity of moving the mold or the die head causes the apparatus to become large.
Further, Japanese Patent Publication No. 4-4931 disclosed a method using a conveyer provided between an extruder and a mold. The method has steps of: placing a parison extruded from the extruder on the conveyer; and moving the conveyer two-dimensionally or three-dimensionally so as to feed the parison into the cavity correctly. The conveyer is moved horizontally (in the X direction and in the Y direction) and if necessary vertically (in the Z direction). However, in this method, the moving speed of the conveyer is slow, and accordingly it takes a long time to deliver the parison to the mold. Moreover, while the parison is being fed into the cavity, the parison may be twisted by curved portions of the cavity (portions 42b and 42c of the cavity 42 shown in FIG. 3 which corresponds to the curved portions 2 and 3 of the hose 1 shown in FIG. 4).
In the blow molding, the temperature of the parison is important. The portions of the parison which are in contact with the conveyer and the mold are cooled more easily than the other portions, and at the time of injection of compressed air, the portions at a lower temperature do not expand so much as the other portions. Consequently, the wall thickness there becomes larger, and the molded product has a varied wall thickness.